Strat makes popping noise.

My '57 RI Strat makes a scratchy popping noise occasionally, but only when I move the guitar body. For instance it makes this noise when I switch the guitar from my right knee to my left or reposition it on my shoulder with the strap on. I thought it was the cord turning in the jack or the jack itself. I replaced the jack and tried several cords with different kinds of connectors and the darn thing still makes this noise. It sounds like something discharging. Once it happens I cannot reproduce it until a few minutes have passed then I can reproduce it. This is why I'm thinking it may be static from the pickguard or something like that. The pickups are original, but I installed the 5 way switch and jumpered the mid pickup tone control lug to the one that allows me to use it for the bridge too. The guitar has been wired like this for a few years, but this noise is a recent development. Any suggestions on a remedy

I took the pickguard off and inspected the connections just to see if anything was loose. I put it back together and it has not happened since. I did notice that there is sheilding only under the controls and not the pickups. It's a wait and see thing I guess. Thanks for asking.